add an option for ddb ps command to print process arguments

We use ps to collect the information of all processes in textdump. But
it doesn't contain process arguments which however sometimes are very
useful for debugging.  The new 'a' modifier adds that capability.

While here, remove 'm' modifier from ddb.4.  It was in the manual page
from its very first revision, but I could not find any evidence of the
code ever supporting it.

Submitted by:	Terry Hu <thu@panzura.com>
Reviewed by:	kib
MFC after:	1 week
Sponsored by:	Panzura
Differential Revision: https://reviews.freebsd.org/D16603

2 files changed, 37 insertions, 11 deletions

diff --git a/share/man/man4/ddb.4 b/share/man/man4/ddb.4
index 6c0d1c1cfdf8..aeec111adefe 100644
--- a/share/man/man4/ddb.4
+++ b/share/man/man4/ddb.4
@@ -537,16 +537,15 @@ If the thread is not found, search the thread stack cache and prints the
 cached stack address.
 Otherwise, prints nothing.
 .Pp
-.It Ic show Cm all procs Ns Op Li / Ns Cm m
-.It Ic ps Ns Op Li / Ns Cm m
+.It Ic show Cm all procs Ns Op Li / Ns Cm a
+.It Ic ps Ns Op Li / Ns Cm a
 Display all process information.
 The process information may not be shown if it is not
 supported in the machine, or the bottom of the stack of the
 target process is not in the main memory at that time.
 The
-.Cm m
-modifier will alter the display to show VM map
-addresses for the process and not show other information.
+.Cm a
+modifier will print command line arguments for each process.
 .\"
 .Pp
 .It Ic show Cm all trace
diff --git a/sys/ddb/db_ps.c b/sys/ddb/db_ps.c
index 0c9687c62fbd..2c7c205785bf 100644
--- a/sys/ddb/db_ps.c
+++ b/sys/ddb/db_ps.c
@@ -50,8 +50,13 @@ __FBSDID("$FreeBSD$");
 
 #include <ddb/ddb.h>
 
+#define PRINT_NONE	0
+#define PRINT_ARGS	1
+
 static void	dumpthread(volatile struct proc *p, volatile struct thread *td,
 		    int all);
+static int	ps_mode;
+
 /*
  * At least one non-optional show-command must be implemented using
  * DB_SHOW_ALL_COMMAND() so that db_show_all_cmd_set gets created.
@@ -62,6 +67,24 @@ DB_SHOW_ALL_COMMAND(procs, db_procs_cmd)
 	db_ps(addr, have_addr, count, modif);
 }
 
+static void
+dump_args(volatile struct proc *p)
+{
+	char *args;
+	int i, len;
+
+	if (p->p_args == NULL)
+		return;
+	args = p->p_args->ar_args;
+	len = (int)p->p_args->ar_length;
+	for (i = 0; i < len; i++) {
+		if (args[i] == '\0')
+			db_printf(" ");
+		else
+			db_printf("%c", args[i]);
+	}
+}
+
 /*
  * Layout:
  * - column counts
@@ -90,6 +113,7 @@ db_ps(db_expr_t addr, bool hasaddr, db_expr_t count, char *modif)
 	char state[9];
 	int np, rflag, sflag, dflag, lflag, wflag;
 
+	ps_mode = modif[0] == 'a' ? PRINT_ARGS : PRINT_NONE;
 	np = nprocs;
 
 	if (!LIST_EMPTY(&allproc))
@@ -207,6 +231,10 @@ db_ps(db_expr_t addr, bool hasaddr, db_expr_t count, char *modif)
 			db_printf("%s", p->p_comm);
 			if (p->p_flag & P_SYSTEM)
 				db_printf("]");
+			if (ps_mode == PRINT_ARGS) {
+				db_printf(" ");
+				dump_args(p);
+			}
 			db_printf("\n");
 		}
 		FOREACH_THREAD_IN_PROC(p, td) {
@@ -299,6 +327,10 @@ dumpthread(volatile struct proc *p, volatile struct thread *td, int all)
 		db_printf("%s", td->td_proc->p_comm);
 	if (p->p_flag & P_SYSTEM)
 		db_printf("]");
+	if (ps_mode == PRINT_ARGS && all == 0) {
+		db_printf(" ");
+		dump_args(p);
+	}
 	db_printf("\n");
 }
 
@@ -445,12 +477,7 @@ DB_SHOW_COMMAND(proc, db_show_proc)
 		db_printf(" ABI: %s\n", p->p_sysent->sv_name);
 	if (p->p_args != NULL) {
 		db_printf(" arguments: ");
-		for (i = 0; i < (int)p->p_args->ar_length; i++) {
-			if (p->p_args->ar_args[i] == '\0')
-				db_printf(" ");
-			else
-				db_printf("%c", p->p_args->ar_args[i]);
-		}
+		dump_args(p);
 		db_printf("\n");
 	}
 	db_printf(" repear: %p reapsubtree: %d\n",